1. Field of the Invention
This invention relates generally to a control system and method for preventing a vehicle-trailer from jackknifing and, more particularly, to a control system and method that selectively controls rear-wheel steering of a vehicle to assist the vehicle operator when backing up a trailer to prevent a jackknife condition.
2. Discussion of the Related Art
Automotive vehicles that employ coordinated front wheel steering and rear-wheel steering systems are known in the art. Typically in such coordinated vehicle wheel steering systems, the driver controls the steering of the vehicle's front wheels and a computer-based on-board steering controller controls the steering of the vehicle's rear wheels in response thereto. In one example, the computer controlled rear-wheel steering system employs an electric motor driven rack and pinion rear-wheel steering actuator.
Backing up a vehicle-trailer is typically a complex task, and requires a certain level of skill. A jackknife condition may occur when a vehicle-trailer is moving away from its equilibrium position, where the system becomes unstable. In other words, the relative angle between the vehicle and trailer is diverging from the driver's intended target angle, which usually increases if proper steering and/or breaking actions are not taken.
It is known in the art to employ the coordinated front and rear wheel steering system referred to above to assist a driver operating a vehicle pulling a trailer. Particularly, U.S. Pat. No. 6,292,094, issued Sep. 18, 2001 to Deng et al., discloses a vehicle/trailer backing-up control system in connection with a computer controlled rear-wheel steering system. The '094 patent employs an algorithm that uses front wheel angle, vehicle speed, vehicle yaw rate and hitch angle to control the rear-wheel steering angle to assist the operator in backing up the vehicle-trailer. U.S. patent application Ser. No. 10/336,120, filed Jan. 3, 2003, titled “Trailer Tongue Length Estimation Using a Hitch Angle Sensor,” is a modification of the '094 patent that provides an estimation of the trailer tongue length to further help the system in the back-up control.
U.S. patent application Ser. No. 10/435,209, filed May 9, 2003, titled “Vehicle Trailer Backing Up Jackknife Detection And Warning System,” assigned to the assignee of this application, discloses a jackknife warning system for a vehicle. This jackknife warning system uses vehicle steering angle, vehicle speed and hitch angle to determine a potential jackknife condition. The system warns the driver if the trailer is moving towards a jackknife condition, and provides steering direction assistance.